The present invention concerns the area of spinal surgery, more precisely the drilling of vertebral pedicles, in particular for setting pedicle screws.
The use of manual or motorized drilling instruments is known, alternatively rotating or mobile around a median position.
In particular European patent EP287823 is known describing a surgical instrument for manual use, especially for osteosynthesis, fitted with a handle to which is attached a tool such as a screwdriver tip or bore, with a shaft having coaxial rotational support within the handle and on which two cogwheels are fixed distant from one another, with a stop pawl arranged in the handle and actuated from outside, and which in one end-stroke position only engages into to the crown wheel of one of the cogwheels, and which at the other end-stroke position only engages into the crown wheel of the other cogwheel.
The problem which arises with the instruments of the state of the art relates to the guiding of the drilling instrument, and more precisely to the choice of entry point and orientation of the drilling tool in order to avoid any risk of going beyond the pedicle.
The difficulty derives from the need to cross through cancellous bone while remaining in contact with cortical bone, it being essential to avoid a pathway that is too lateral which could injure the spinal cord or the spinal nerves.
The difficulty is further increased if the pedicle is deformed requiring the drilling instrument to emerge at one point of the pedicle and to return inside the pedicle beyond the deformation without harming innervated parts.
Clinical trials show that that no satisfactory solution has been found to this problem at the present time, and it would appear that 25% of pedicle screws are ill-positioned.
To meet this problem, the invention consists of detecting a nerve or nerves by electrifying the drilling instrument.
It is true that the prior art contains documents concerning the detection of muscular response by analysis of an electric signal. But the end purpose of such equipment is the monitoring of nerve activity, in particular during anaesthesia.
American patent U.S. Pat. No. 5,284,153, for example, is known. This document discloses and claims a method for locating a nerve. It suggests several steps including the determination of the distance between the nerve and stimulation means. This step is of no interest in bringing an answer to the problem of guiding an instrument for drilling a vertebral pedicle.
American patent U.S. Pat. No. 5,779,642 discloses a method of locating a nerve for guiding a puncture needle, which uses a needle-locating step by means of ultrasound. Patent U.S. Pat. No. 4,824,433 also concerns an application for positioning a puncture needle, through the use of an electric current supplying the needle and the detection of this signal.
Patent U.S. Pat. No. 4,962,766 discloses equipment for locating nerves during surgery. The purpose is the study of nerve function.
None of these documents expressly concerns, nor suggests, the guiding of a drilling instrument for drilling a vertebral pedicle.
American patents U.S. Pat. Nos. 5,196,015 and 5,474,558 are also known, concerning a method for inserting a pedicle screw, according to which the evoked potential is detected at the time of insertion of a pedicle screw. Detection of patient reaction is made by visual observation, which cannot guarantee a sufficiently fast reaction on the part of the surgeon. In addition, the trigger threshold of the reaction is dependent upon the patient, upon patient condition, and cannot guarantee satisfactory reliability and sensitivity in detection.
The invention, in its more general sense, concerns equipment for drilling bone, in particular for setting a pedicle screw in accordance with claim 1.
The equipment of the invention comprises a drilling instrument, a source of electric impulses and means for connecting the electric impulse source to the drilling instrument. The equipment also comprises at least one sensor for detecting a muscle signal intended to be implanted in a muscle or placed on the skin in the vicinity of a muscle before drilling is started and during drilling, and means to produce an alert in the event of detection by at least one sensor of a muscle signal correlated with the electric impulse source connected to the drilling instrument.
The electric impulses are of fixed frequency and the alert means is triggered whenever the detected signal has identical frequency to the frequency of the electric impulses.
According to one variant, the means of alert is a sound and/or tactile and/or light signal.
According to one particular embodiment, the source of electric impulses connected to the drilling instrument delivers a signal in the form of impulses having a frequency of 5 hertz or less.
According to a first variant, the source of electric impulses is connected to the drilling instrument by means of an electric cord.
In a second variant, the source of electric impulses is positioned inside the drilling instrument.
The sensor or sensors is or are connected to the drilling instrument by means of an electric cord.
The invention also concerns an instrument for drilling bone, in particular for drilling a vertebral pedicle, intended to prepare the pedicle prior to setting a pedicle screw.
According to one particular variant, the means for connecting the drilling instrument to the source of electric impulses is formed of a rotating connector.
The invention also concerns a control device for the bone drilling equipment according to the invention.
According to one particular variant, the control device comprises an output connectable to the drilling tool and a detection circuit whose output is connectable to at least one sensor.
According to another particular variant, the control device is incorporated in a handle of the drilling instrument.
The invention further concerns an assembly made up of two sensors of a particular type, electric sensors, for bone drilling equipment according to the invention in which said sensors are positioned at invariable distance from one another.
The invention further concerns a method for drilling bone, vertebral pedicles in particular, for setting in place a pedicle screw using drilling equipment which comprises:
a manual or motorized drilling instrument able to drive a drilling tool in rotation,
a source of electric impulses and means for connecting the electric impulse source to the drilling instrument, and
at least one sensor to detect a muscle signal intended to be implanted in a muscle or placed on the skin in the vicinity of a muscle and connected to a control device,
in which said source of electric impulses sends electric impulses into said drilling tool, and in which, throughout drilling, said control device analyses the signal received from at least one detection sensor, and uses an alert-producing means in the event of detection by at least this sensor of a muscle signal correlated with the source of electric impulses connected to the drilling instrument.
According to one preferred embodiment, the entry point or orientation of the drilling instrument is modified in the event that the alert means is triggered.